Abstract

Cement-sheath integrity is fundamentally important for well integrity and helps to ensure that the asset is operated safely and economically. If the cement sheath is damaged during well operations, it could lead to interzonal communication, annular pressure, and casing damage. Remedial jobs are then necessary to fix the problem and continue well operation. In some cases, it might not be economical to fix the problem, leading to well abandonment.

The challenge to cement-sheath integrity is caused by the stresses resulting from change in pressure and temperature during well operation. Examples of wells that could be subjected to changes in pressure and temperature are deepwater, high-pressure high-temperature (HPHT), gas storage, steam injection, and geothermal. Gas storage wells in Italy are addressed in this work. An integrated, intelligent, and interventionless solution has been applied to solve the zonal-isolation challenges in such wells. The well events during the life cycle were integrated into the analysis and a cement sheath was designed and tested so that it was not damaged. Safety considerations were built into the design procedures based on the teachings of designs of other materials. This design procedure helped the cement sheath withstand cyclic loads, which could be significant in gas storage wells.

During well operations, if the stresses on the cement sheath exceed the design limits, the cement sheath could be damaged. The initial damage could be in the form of small cracks and micro-annuli. If these damages can be fixed immediately and without intervention, then the formation fluid can be prevented from entering the annulus. Intelligent features were built into the cement sheath so that small cracks and micro-annuli could be automatically sealed if formation fluid enters the annulus.

The integrated, intelligent, and interventionless zonal-isolation features of the solution offer a unique opportunity to prevent the annular pressure buildup if the cement sheath inadvertently fails. This solution has been implemented in a number of wells and is described in this work. The job implementation and subsequent results during the life of the wells have been successful. The unique features of the solution discussed and presented in this work is a game-changer and should help the industry solve a pressing problem and operate wells safely and economically.

Introduction

Storing natural gas during times when the demand is low and using it when the demand is high is a common industry activity. This procedure is followed in a number of countries around the world. The inherent nature of the process employed causes change in pressure and temperature during gas injection and then during gas production (gas withdrawal). It is important to maintain cement-sheath integrity so that the injected gas is contained and does not flow up the annulus to the surface or to another zone.

Most of the gas storage wells are located close to the end customer. Therefore, from a health, safety, and environmental aspect it becomes extremely important to contain the injected gas and prevent leakage. Though best practices were used, zonal isolation was a challenge in the wells that were cemented before the techniques discussed in this work were applied. As shown in Fig. 1, 63% of the wells in Field B showed sustained casing pressure (SCP). This number was lower in Field A and C; however, SCP was still in the double digits. As a result, a campaign was undertaken to investigate the challenges and improve the reliability of zonal isolation.

This content is only available via PDF.
You can access this article if you purchase or spend a download.